1. Field of the Invention
The invention relates to a hybrid vehicle equipped with an internal combustion engine and a motor-generator for running the vehicle, and more particularly to a hybrid vehicle provided with an electrical heated catalyst (EHC) in an exhaust passage of the internal combustion engine.
2. Description of Related Art
A vehicle equipped with an internal combustion engine is typically provided with a catalyst for purifying the exhaust gas of the internal combustion engine. The catalyst cannot purify the exhaust gas sufficiently unless the activation temperature of the catalyst is reached. Accordingly, an EHC configured such that the catalyst can be heated by an electrical heater or the like has been suggested.
Japanese Patent Application Publication No. 2009-274479 (JP-2009-274479 A) discloses the configuration of an electric system used when an EHC is provided at a hybrid vehicle in which an on-board power storage device can be charged from a power source installed outside of the vehicle (referred to hereinbelow as “external power source”). The catalyst temperature in the EHC is raised by heat generation by energization during actuation. Charging of the onboard power storage device with an external power source will be referred to hereinbelow simply as “external charging”.
JP-2009-274479 A discloses the configuration of an electric system for energizing an EHC by using a charger for external charging. More specifically, the configuration is disclosed in which the EHC is connected in parallel to the primary winding or secondary winding of a transformer in a charger constituted by an insulating power converter including the transformer.
Since the EHC is disposed in the exhaust passage of the engine, electrical abnormalities caused by the decrease in insulation resistance can occur under the effect of soot or water. In the configuration disclosed in JP-2009-274479 A, the insulation between the power storage device and the EHC can be ensured by connecting the EHC in parallel with the secondary winding of the transformer.
However, in the configuration disclosed in JP-2009-274479 A, the EHC is not provided with a circuit for detecting the decrease in insulation resistance (referred to hereinbelow as “current leakage detection circuit”) when the vehicle is used. Therefore, where the insulation resistance of the EHC temporarily decreases under the effect of soot or water, it is possible that the occurrence of such decrease will not be detected.
Further, in order to detect the decrease in insulation resistance of the EHC with the circuit configuration ensuring the insulation between the power storage device and the EHC, it is necessary to install a current leakage detection circuit separately from the circuit system connected to the power storage device. As a result, the cost can be increased.